As the Asteroid Turns: Hubble Records New Video of 2nd Biggest Space Rock

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New views of the second-biggest asteroid in the solar system are
giving astronomers a better sense of how the object spins
information that will come in handy when a NASA spacecraft
arrives at the space rock July 2011.

The images, taken by the Hubble Space Telescope, show the
asteroid Vesta, a large space rock in the asteroid belt located
between the orbits of Mars and Jupiter.

The images show that Vesta has a tilt of approximately 4 degrees
more to the asteroid's east than scientists previously thought.
The data, researchers said, will help NASA plan the arrival of
the
unmanned Dawn spacecraft at Vesta next year.

"While Vesta is the brightest asteroid in the sky, its small size
makes it difficult to image from Earth," said Dawn mission
science team member Jian-Yang Li, of the University of Maryland
in College Park, in a statement. "The new Hubble images give Dawn
scientists a better sense of how Vesta is spinning, because our
new views are 90 degrees different from our previous images. It's
like having a street-level view and adding a view from an
airplane overhead."

New spin on Vesta

The new spin and tilt information suggest that seasonal
conditions in Vesta's southern and northern hemispheres may take
place about a month later than previously expected when Dawn is
orbiting.

The
asteroid Vesta is about 329 miles (529 km) wide and second in
size only to Ceres, a huge space rock in the asteroid belt that
is so large it qualifies as a dwarf planet. The Dawn spacecraft
will visit both asteroids, starting with Vesta, to get close-up
look at the huge rocks.

The goal of Dawn's mission is to take images of the entire
surface of the asteroid and to measure the elevation over most of
the surface to an accuracy of about 33 feet (10 m), or the height
of a three-story building.

Knowing about the extra tilt is important because it affects the
pattern of sunlight Vesta will receive.

"The new results give us food for thought as we make our way
toward Vesta," said Christopher Russell, Dawn's principal
investigator at UCLA. "We need to pay close attention to the
solar illumination. It looks as if Vesta is going to have a late
northern spring next year, or at least later than we planned."

The new images, captured by Hubble's Wide Field Camera 3 in
February, complement previous images of Vesta taken from
ground-based telescopes and Hubble's Wide Field and Planetary
Camera 2 between 1983 and 2007.

The new analysis was detailed in a recent online edition of the
journal Icarus.

The spacecraft will enter polar orbit around the 330-mile
(531-km) wide Vesta and stay there until May 2012 before moving
on to the Texas-sized Ceres, which it should reach by February
2015.

Vesta and Ceres are the most massive objects in the main asteroid
belt between Mars and Jupiter. Spherical Ceres is the only
asteroid large enough to be considered a dwarf planet, making
Dawn the first mission to a dwarf planet.

Scientists study these celestial bodies as examples of the
building blocks of terrestrial planets like Earth. NASA also
expects that close examinations of space rocks will help the
agency plan its next mission of sending astronauts to visit an
asteroid by 2025.